Changes in the axons and myelin sheaths of the Syrian hamster mutant with hind leg paralysis will be studied with the light and electron microscope. Our plan is to investigate (1) the relationship between the axonal and Schwann cell changes, (2) the origin of filaments and crystalloid formation, the so-called Hirano bodies, already observed in these animals, (3) the connection between these changes and demyelination, and (4) the changes in the anterior horn cells, if any, in the chronic stages of the disease and its relevance to familial amyotrophic lateral sclerosis.